As the reserves of conventional crude oils decline, heavy oils must be upgraded to meet world demands. In heavy oil upgrading, heavier materials are converted to lighter fractions and most of the sulfur, nitrogen and metals must be removed. Heavy oils include materials such as petroleum crude oil, atmospheric tower bottoms products, vacuum tower bottoms products, heavy cycle oils, shale oils, coal derived liquids, crude oil residuum, topped crude oils and the heavy bituminous oils extracted from oil sands. These heavy hydrocarbon feedstocks may be generally characterized by low reactivity, high heteroatom and metal content, high coking tendency, poor susceptibility to hydrocracking and difficulties in distillation. Most residual oil feedstocks which are to be upgraded contain some level of asphaltenes which are commonly known to be heptane insoluble compounds as determined by ASTM D3279 or ASTM D6560. Asphaltenes are high molecular weight compounds containing heteroatoms which impart polarity.
Heavy oils must be upgraded in a primary upgrading unit before they can be further processed into useable products. Primary upgrading units known in the art include, but are not restricted to, coking processes, such as delayed or fluidized coking, and hydrogen addition processes such as fixed bed resid hydrotreating, ebullated bed or slurry hydrocracking (SHC).
In SHC, a three-phase mixture of heavy liquid oil feed cracks in the presence of gaseous hydrogen over solid catalyst to produce lighter products under pressure at an elevated temperature. The catalysts for SHC are typically metal sulfides derived from transition metal based precursors. Iron, molybdenum, nickel, cobalt and tungsten are among typical examples.
SHC products require hydroprocessing to be used as final products. They are generally high in heteroatom content, primarily nitrogen and sulfur, and require hydroprocessing to remove these contaminants. Commonly, aromatic ring saturation is also required to meet product specifications. To sell the product as a premium product, e.g., Euro 5 diesel or gasoline, could require extreme conditions, large catalyst volume or high activity catalysts to refine.
SHC products have a broad range of boiling points with widely varying properties. Because these products do not require the same hydroprocessing severity, e.g. pressure, temperature and residence time, typically each fraction is hydroprocessed separately. As a result, hydroprocessing units are highly expensive in terms of capital investment.
Therefore, there is strong economic incentive to integrate the hydroprocessing of different fractions having different properties, either in reduced reaction steps, or by reducing the common equipment, e.g., the fractionation section and/or the hydrogen compression system. The key benefit is significant cost savings and achieving comparable, if not improved, product properties by using an integrated hydroprocessing system.